[PATCH] nfsd: free nfsd_file by gc after adding it to lru list

[Li Lingfeng <lilingfeng3@huawei.com>]

In nfsd_file_put, after inserting the nfsd_file into the nfsd_file_lru
list, gc may be triggered in another thread and immediately release this
nfsd_file, which will lead to a UAF when accessing this nfsd_file again.

All the places where unhash is done will also perform lru_remove, so there
is no need to do lru_remove separately here. After inserting the nfsd_file
into the nfsd_file_lru list, it can be released by relying on gc.

Fixes: 4a0e73e635e3 ("NFSD: Leave open files out of the filecache LRU")
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
---
 fs/nfsd/filecache.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index a1cdba42c4fa..37b65cb1579a 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -372,18 +372,10 @@ nfsd_file_put(struct nfsd_file *nf)
 		/* Try to add it to the LRU.  If that fails, decrement. */
 		if (nfsd_file_lru_add(nf)) {
 			/* If it's still hashed, we're done */
-			if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
+			if (list_lru_count(&nfsd_file_lru))
 				nfsd_file_schedule_laundrette();
-				return;
-			}
 
-			/*
-			 * We're racing with unhashing, so try to remove it from
-			 * the LRU. If removal fails, then someone else already
-			 * has our reference.
-			 */
-			if (!nfsd_file_lru_remove(nf))
-				return;
+			return;
 		}
 	}
 	if (refcount_dec_and_test(&nf->nf_ref))
-- 
2.31.1